1. Field of the Invention
The present invention relates to an apparatus and a method of extracting an equivalent circuit of a T-type transmission circuit having an AC current ground terminal, and first and second terminals for signal transmission.
2. Related Art
There are a number of known techniques related to an inductor model formed on a semiconductor substrate. Such known techniques relate to an equivalent circuit assuming a two-terminal structure having one input terminal and one output terminal (for example, refer to John R. Long and Miles A. Copeland, “Modeling of Monolithic Inductors and Transformers for Silicon RFIC Design”, MTT-S 1995 International Topical Symposium pp. 129-134).
The above document discloses the following. When the inductor model is constructed, a large number of impedances of elements formed on a silicon substrate is actually measured with a network analyzer, or the like; the measured values are converted to four-terminal equivalent circuit parameters (i.e. Y parameter or Z parameter), or the like; and in consideration of a configuration of the equivalent circuit, equivalent circuit values (i.e. values of elements such as an inductor and a resistor used in the above equivalent circuit) of the equivalent circuit are extracted.
Recently, the inductors are frequently utilized in a three-terminal structure. For example, the inductors are utilized in a structure having a center-tap in a Voltage Controlled Oscillator (VCO), and are utilized in a configuration for an ON-Chip transformer. In addition, there are increased needs to easily and accurately extract the equivalent circuit values of a three-terminal inductor as there are increased instances where an electromagnetic analysis is utilized to estimate the inductor characteristics.
In an equivalent circuit value calculating method described in the above document, it is assumed that the two-terminal inductor is used. Therefore, this method can not be directly used to extract the equivalent circuit values of the three-terminal inductor, which is a significant problem.
As a method for extracting the equivalent circuit value, there is a known method in which a measured value or an electromagnetic field analysis calculated value are used as a reference value, the equivalent circuit value is swept on a simulator, and a combination of values which are the closest to the measured value is obtained. This method, however, has a problem that the obtained result depends on an initial value utilized or an operator of the simulator, and it is not possible to accurately determine whether or not the obtained result is physically correct.
In addition, there is a latest simulator having a program in which the circuit configuration and the equivalent circuit value which are the most suitable to the targeted S parameter are automatically combined to generate the equivalent circuit. It is not assured for the same reason as the above that a circuit designer can obtain significant information in a short period.